1. Field of Invention
The field of the currently claimed embodiments of this invention relates to electro-optic devices, and more particularly to polarizing photovoltaic components and devices that incorporate the components.
2. Discussion of Related Art
Liquid crystal display (LCD) technology is currently the most popular information display technology. Its uses include monitors for computers, laptops, televisions, instrument panels, projectors, and other electronic devices ranging from aircraft cockpit displays to every-day consumer electronic devices.
Generally, each pixel of the LCD consists of four basic components: backlight units, back polarizing filter, a layer of aligned liquid crystal molecules between two transparent electrodes, and front polarizing filter. FIG. 1 shows the basic construction of a pixel in an LCD display. The isotropic backlight can be divided into two linear oscillation components: the parallel (//) and perpendicular (+) polarizations. Usually, a polarizer is formed by stretching a linear long-chain organic (or polymeric) molecule into a uniaxial orientation. When unpolarized light (with both // and + polarizations) falls on the polarizer, the stretched molecules absorb photons with electric field oscillation parallel to the stretch direction. This is defined as the parallel polarization. When the light reaches the back polarizing film, the // polarization (with respect to the back film) is absorbed, and only the perpendicularly polarized light can pass through the polarizer. The orientation of the front and back polarizer is perpendicular to completely cross-out the light to provide a dark background of the display. Without a liquid crystal molecular layer between the polarizing filters, light passing through the back polarizing filter would be blocked by the front one. The electric field-driven liquid crystal molecular layer acts as a light modulator to reorient the direction of the incident linear polarized light. Before applying an electric field, the liquid crystal molecules arrange themselves in a helical or twist structure. This rotates the axis of the incident linear polarized light making it perpendicular to the stretching direction of the front film. Hence, some portion of the light can pass thought the front polarizing film resulting in a grey pixel. After applying an electric field, the liquid crystal molecules are almost completely untwisted and the polarization direction of the linear polarized incident light is not rotated as it passes through the liquid crystal layer. This light will then be blocked by the front filter, resulting in a black pixel. By modulating the bias applied on the liquid crystal layer, the portion of light passed can be varied, which constitutes different levels of gray.
From the energy point of view, LCD technology is very inefficient. The power consumption of the backlight unit is the largest portion of the total power consumption in an LCD. To add to it, more than 90% of light energy from the backlight unit is absorbed by the two orthogonal polarizing filters. That is a great waste of energy, especially when the pixel is black since the LCD's backlight is always on so the light energy for a black pixel is 100% wasted. There thus remains a need for improved polarizers and devices that incorporate the improved polarizers.